Audio accumulator



Sept. 27, 1966 D. E. HANSEN AUDIO ACCUMULATOR 2 Sheets-Sheet 1 FiledFeb. 27, 1964 QTTOENEYS.

I IF For mm p 27, 1966 D. E. HANSEN 3,276,006

AUDIO ACCUMULATOR Filed Feb. 27, 1964 2 Sheets-Sheet 2 m- INPUT SIG NALI l I l I I I RELAY VOLTS I I INPUT SIGNALS TIME 125 31 CHARGE TIME.

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United States Patent 3,276,006 AUDIO ACCUMULATOR Donald E. Hansen,Brookfield Center, Conn., assignor to Mosier Research Products, Inc.,Danhury, C0nn., a corporation of Delaware Filed Feb. 27, 1964, Ser. No.347,761 1 Claim. (Cl. 340-261) This invention relates to security alarmsand is particularly directed to an audio accumulator for use inconnection with alarms adapted to be set off by noise or vibration.

One common form of alarm system used to protect bank vaults and otherareas to be secured is an audio alarm. In such an alarm, a microphone,speaker, vibration pickup or the like, senses noise such as might beproduced by a burglar tampering with a lock, cutting an opening in awall or the like. When such a noise occurs, an alarm is tripped eitherlocally or in a remote station providing warning that a robbery or othertrespass is being attempted.

One of the most difficult problems in connection with audio alarms isproviding means for distinguishing between noise accompanying anattempted surreptitious entry and ambient or background noise caused byinnocent activity, such as for example by passing vehicles, movingpeople or objects in adjacent areas or the like.

The principal object of the present invention is to provide an audioaccumulator circuit which is highly effective to distinguish betweennoise or vibration caused by an attempted intrusion and background noisenot connected with such intrusion. In essence, then, the present audioaccumulator is effective to cause the alarm to be actuated whenever anintruder is attempting to enter the secured area, but at the same timeis effective to prevent spurious or false alarms caused by ambientnoise.

More particularly, the present invention is predicated upon the conceptof providing an accumulator circuit which is effective to causeactuation of the alarm only when a certain quantum of noise is sensed,i.e. a level of noise persisting for a definite time. Specifically, thepresent accumulator includes means for integrating the noise sensed,both with respect to amplitude and time. The unit operates so that aselected noise will cause an alarm if the noise persists for apredetermined time, for example one tenth of a second. A lesser noise ofonetenth the amplitude will cause an alarm only if it persists forapproximately one second; and a larger noise, say ten times theamplitude of the selected noise, will cause an alarm if the noisepersists for only one-hundredth of a second.

Another object of the present invention is to provide means forautomatically resetting the accumulator or continuously wiping itsmemory clean of events occurring more than a predetermined time in thepast. This resetting, or memory wiping, means thus prevents the alarmfrom being actuated in response to the sensing of a plurality of widelyspaced low level noise signals. By way of example, in a giveninstallation there might normally be ten ambient noise events, such asvehicles passing by, doors closing and the like, per hour. However, iften events of the same level occur within a minute, it would most likelyindicate an attempted intrusion. The present audio accumulator iseffective to differentiate between the two and to cause an alarm in thelatter instance but not in the first instance.

A still further object of the present invention is to provide anelectronic, and in a preferred embodiment, solid state audio accumulatorwhich is of relatively simple construction and high reliability in use.

These and other objects and advantages of the present invention will bemore readily apparent from a consid- 3,276,6 Patented Sept. 27, 1966eration of the following detailed description of the drawingsillustrating one preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a schematic circuit diagram showing an alarm systemembodying a preferred form of sound accumulator.

FIGURE 2 is a diagrammatic view showing the operation of the circuit inresponse to the occurrence of a single audible event.

FIGURE 3 is a diagrammatic view showing the operation of the circuit inresponse to the occurrence of a plurality of audible events.

As is shown in FIGURE 1, one form of alarm system embodying theprinciples of the present invention comprises a sound, or vibration,detector located in the area to be protected, such as a vault or thelike. The sound, or vibration, detector 10 may be in the form of amicrophone, speaker, or vibration microphone. The pickup device, ordetector 10 is connected through a twisted pair of leads 11 and 12,forming part of a shielded cable, to audio accumulator circuit 13. Itwill, of course, be appreciated that this audio accumulator circuit 13may be located either in or at a point remote from the area to beprotected as desired. The audio accumulator circuit 13 is effective tocontrol the energization of a relay 14 which in turn controls theactuation of an electrically responsive alarm indicated at 15.

More particularly, lead 11 from the transducer 10 is connected to thebase 16 of a transistor 17 forming part of the first stage of theaccumulator unit. This stage is a generally conventional common emitteraudio amplifier stage. Lead 12 is similarly connected to the emitter 18of transistor 17 through series connected resistors 20 and 21. Each ofthe resistors 20 and 21 is shunted by a capacitor 22 and 23respectively. A sensitivity adjustment resistor 24 is connected betweenleads 11 and 12. The other components of this first stage comprise aresistor 25 interconnecting base 16 and collector 26. A positivepotential source indicated at 27 is connected to resistor 21 throughlead 28, resistor 30 and lead 31. Lead 31 is connected through acapacitor 32 to a common line 33. Line 33 is connected at one endthrough a resistor 34 to lead 12. The opposite end of line 33 is joinedto normally closed contact 35 of relay 14.

The first amplifier stage of the audio accumulator unit is transformercoupled to the second stage which is also a common emitter stage of agenerally conventional type used in audio amplifiers. Specifically,collector 26 of transistor 17 is connected to one lead of primarywinding 36 of coupling transformer 37. The opposite lead of winding 36is connected through lead 38 to common line 33. Secondary winding 40 ofcoupling transformer 37 is connected across a sensitivity adjustmentpotentiometer 41. Secondary winding 40 is also connected through lead 39and resistor 42 to lead 38.

Tap 43 of potentiometer 41 is connected to base 44 of transistor 45. Alead 46 is connected to lead 39 and one end of potentiometer coil 41 andto the parallel combination of resistor 47 and capacitor 48. Resistor 47is in turn joined through the parallel combination of resistor 50 andcapacitor 51 to an emitter 52 of transistor 45. A lead 53 is connectedto resistor 50 and to a resistor 54 which is in turn joined through lead55 to a source of positive potential indicated at 56. A capacitor 57interconnects lead 53 and line 33. A capacitor 58 is connected betweencollector 60 of transistor 45 and one terminal of potentiometer 41.

This second stage of the sound accumulator unit is transformer coupledto the third stage of the unit which functions as a detector. Moreparticularly, the collector 60 of transistor 45 is connected to primarywinding 61 3 of coupling transformer 62. This primary winding is alsoconnected through lead 63 to common line 33. The secondary winding 64 oftransformer 62 is connected to 'base 65 of transistor 66. Transistor 66further includes .an emitter 67 joined through lead 68 to common line33. .The collector 70 of transistor 66 is connected through lead 71,resistor 72 and lead 73 to a positive potential source indicated at 74.

This third stage of the audio accumulator unit oper- ..ates saturated.Thus, the full supply voltage from source 74 is dropped across collectorresistor 72. It is to be .noted that lead 73 is joined through arectifier 75 to lead applied to" the fourth; or decoupling, stage of theunit.'

Specifically, collector 70 is connected through lead '71, rectifier 8'1and lead 82 to base 83 of transistor 84. Lead 82 is also connected to abias line 85 through the parallel combination of resistor 86 andcapacitor 87. Line 85 is in turn joined through lead 88 to a source ofnegative potential indicated generally at 90. An emitter load resistor91 is connected between line 85 and emitter 92 of transistor 84. Theemitter 92 is also connected through resistor 93 and rectifiers 94 and95 to the base 96 of transistor 97.

This transistor 97 forms part of the fifth stage. Collector 98 oftransistor 84 is connected through lead 100 to collector 101 oftransistor 97. Lead 100 is also tied to positive potential source 74. Acharging capacitor 102 is connected through lead 103 to the juncture ofdiodes 94 and 95 and through lead 104 to line 85. Line 85 is also tiedthrough capacitor 105 to the secondary winding 64 of couplingtransformer 62. This same secondary vwinding is also tied to lead 11through resistor 106 and lead 107.

Base 96 of transistor 97 in the fifth stage is connected to line 85through capacitor 108. The emitter 110 of .transistor 97 is connectedthrough lead 111 to the winding 112 of relay 14. The other lead ofwinding 112 is connected to line 85 and negative potential source 90.The fifth stage, including transistor 97, is connected as a commoncollector amplifier and as such is generally analogous to a cathodefollower of vacuum tube circuitry. The load in the form of relay coil112 is connected in the emitter lead and therefore the stage has novoltage gain. However, the base input resistance is equal to the productof the emitter resistance multiplied by the current gain of the stage.This makes it possible to use a capacitor 102 approximately fifty timessmaller than if the stage were omitted and relay 14 energized directly.

Relay 14 has, in addition to stationary contact 35, a normally openstationary contact 113 and a movable contact arm 114. Movable contactarm 114 is connected through lead 88 to negative potential source 90.Contact 113 is joined to output lead 115 of the accumulator. Lead 115 isconnected through rectifier 116 to alarm 15. Rectifier 116 is alsoconnected through a second rectifier 117 to conductive switch element118 which may be in the form of a flexible lead. Conductor 118 isadapted to complete a circuit to contact 120 or contact 121. Cont-act120 is joined through resistor 122 to lead .71. Contact 121 is joinedthrough resistor 123 to lead 103. It is to be understood that in thenormal operation of the unit, conductor 118 engages either contact 120or contact 12 1, depending upon the type of operation desired. If uponalarm the unit is to latch in that con- .dition, conductor 118 isconnected to contact 120. If

the unit is to reset itself shortly after an alarm, conductor '118 isconnected -to contact 121. When conductor 118 is in engagement withcontact 120 and relay 14 is energized, contact 114 is removed fromcontact 35, thereby removing battery negative from lead 33 and emitter67 discharge as shown by line 132. It

of transistor 70. Positive battery current flow is now from lead throughresistor 72, resistor 122, conduct-or 11-8, contact and diode 117 tolead 115, contact 113 and contact 114 to battery negative. The volt ageestablished by resistors 72 and 122 turns on transistor 84 which turnson transistor 97 and holds relay 14 energized. Reset is accomplished byremoval of battery voltage.

When conductor 118 is in engagement with contact 121 and relay '14 isenergized, the accumulator capacitor 102 is discharged through resistor123, contact 121, conductor 1'1'8, diode 117 and relay contacts 113, 114to battery negative. Diode 95 blocks discharge of capacitor 108 throughthe above path. Capacitor 108 discharges through transistor 97, holdingrelay 14 energized until capacitor 102 is fully discharged. i

The operation of the present accumulator circuit can best be understoodfrom a consideration of FIGURE 1 in conjunction with FIGURES 2 and 3.FIGURE 2 illustrates the operation of the circuit in response to asingle audible event. When the accumulator unit is in normal operationand senses only a minimal noise level below. a preselected thresholdvalue, the third stage of the unit, i.e., the stage including transistor66, is operating saturated so that the full voltage from supply source74 is dropped across resistor 72. Consequently, transistor 84 of stagefour is normally nonconducting because of the zero volt potentialpresent on its base 65. (The diode 81 is effective to reject all signalssensed by pickup 10 which are below the selected threshold level.)

When an audio signal above threshold level, such as is indicated bypulse 125, is received a negative pulse is applied to the base 65 oftransistor 66. This causes the transistor to drop out of saturation.Thus, the potential applied to diode 81 and hence base 83 is raised.This positive signal passes through the diode and is smoothed bycapacitor 87.

When a positive potential is applied to base 83, transistor 84 of stagefour becomes conductive. Consequently, a current flows through emitterload resistor 91. A voltage is developed across this resistor whichbegins changing timing capacitor 102 through resistor 93 and diode 94.The combination of resistor 93 and capacitor 102 have a charge time asindicated by line section 126 in FIGURE 2. Input signal is thusintegrated with respect to time and amplitude. The function of diode 94is to prevent capacitor 102 from discharging back through resistors 93and 91 when the positive signal of resistor 91 ceases. I

If the charge on capacitor 102 is sufiiciently high, the fifth stagetransistor 97 permits suflicient current to flow through Winding 112 ofrelay 14 to close that relay. This brings movable contact arm 114 intoengagement with stationary contact 113 completing a circuit to alarm 15.

If, however, at the conclusion of the input signal 125 the charge oncapacitor 102 is not sutficient to cause relay -14 to close, theaccumulator unit automatically begins to wipe its memory as the chargeon capacitor 102 decays by discharge through base 96. After a sufficientdischarge time, the charge across capacitor 102 is completely dissipatedso that the accumulator unit is in effect reset" or its memory is wipedclean.

The operation of the unit when subjected to a series of input signals ofshorter duration is shown in FIGURE 3. As there shown, the first inputsignal 127 causes capacitor 102 to charge in the manner explained above.However, the charge left by this capacitor is not sufiicient to triprelay 14. At the end of the first event 127, the capacitor 102 starts todischarge as indicated by line 128. When the second event 130 occurs,the capacitor again begins to charge as indicated by line 131. At theconclusion of the second event, the charge on the capacitor may stillnot be sutficient to trip relay 14. Again, at the conclusion of event130, capacitor 102 begins to is to be noted, however, that when thethird event 133 occurs, the capacitor has not completely discharged andhence is starting with an elevated charge which is further increased dueto event 133. The signal due to event 133 may be sufficient to raise thecharge on capacitor 102 to a point where relay 14 becomes conductive andalarm 15 is energized. If at the end of the third event a charge oncapacitor 102 is still not sufficient, the capacitor discharges in themanner explained above until it is brought back to a zero potential.

From the foregoing disclosure of the general principles of the presentinvention and the above description of a preferred embodiment, thoseskilled in the art will readily comprehend various modifications towhich the invention is susceptible. Therefore, I desire to 'be limitedonly by the scope of the following claim.

Having described my invention, I claim:

In an alarm system including an audio or vibration pickup effective toproduce an electrical signal and alarm means, the combination of adetector for said electrical signal, a buffer transistor connected tosaid detector, an audio amplifier transistor including a base and anemitter, a series circuit comprising an integrator resistor, and firstand second rectifiers for conducting current in one directioninterconnecting said detector and the base of said audio amplifiertransistor, an integrator capacitor for receiving a charge through saidfirst diode interconnected between the junction of said first and secondrectifiers and a reference potential, a second capacitor connectedinter-mediate said second rectifier and the base of said amplifiertransistor for receiving a charge through said second diode, a relayincluding a winding interconnected to the emitter of said amplifiertransistor, said relay having first and second stationary contacts and amovable contact connected to said reference potential, said movablecontact being in engagement With said first contact when said relay isdeenergized and being in engagement with said second contact when saidrelay is energized, a second resistor connected to the junction of thefirst and second rectifiers for regulating the discharge of saidintegrator capacitor at a first rate, a selectively operable switchetfective to interconnect said second resistor to the second contact ofsaid relay, said second capacitor having a discharge circuit throughsaid amplifier emitter for discharging therethrough at a second rateslower than the rate of discharge of said integrator capacitor, wherebywhen said selectively operable switch interconnects said second resistorand second relay contact and said relay is energized, said integratorcapacitor is fully discharged prior to the discharge of said secondcapacitor and deenergization of said relay.

References Cited by the Examiner UNITED STATES PATENTS 2,435,996 2/1948Baird 340-258 2,655,645 10/1953 Bagno 340-258 X 2,767,393 10/1956 Bagno340258 2,942,247 6/1960 Lineau 340261 X 3,017,543 1/1962 Hillman317148.5 3,134,970 5/1964 Kelly .a 340261 3,147,467 9/1964 Laakman340-261 NEIL C. READ, Primary Examiner.

R. M. GOLDMAN, Assistant Examiner.

